So, here's what I have [and what I have used] on the rb pro sd: 37, [50], 65, 90, 127 KL, 150 SF, 180 KL, 210 KL apo, 360. All are/were the newest models, except the 360 is an oldie. Of those the only one that disappointed me was the 50; it did not have good corner sharpness and also had significant distortion. This was best seen with the 6x8 back; if you cropped in a bit then it probably wouldn't matter so much, but I use the 6x8 back routinely.
Though it is probably an unfair comparison, I once compared the rb 50 to the 50 on my mamiya 6 and that just trashed the rb 50 utterly. Really no comparison at all. Night and day. After that I traded away the rb 50, and purchased an rz pro 2 just to get the 50 uld. Then I depinned an rz 110/2.8 and I use that on the rb for close focus, it is a very nice little thing, too bad it's not in the standard rb lineup.
When I first bought the rb, I used a 127 and loved it immediately. I see no weakness in this lens whatsoever. The 90 is also super, but I prefer the 127. I only use the 90 for one specialized purpose: it mates to a silly 360 degree gizmo that I use from time to time. I have no complaints with the 90 except that when you compare it to the 110/2.8, you think, damn, the 90 is one big ass lens and it isn't very fast! Oh well :rolleyes:
The 180 has, in my opinion, a really hard task up against the 210 kl apo. The 210 is the shortest apo in the rb line and I can report that it is spectacularly, jaw-droppingly sharp, and still with that characteristically smooth OOF rendering that mamiyans value.
Now, I am not one to shoot test charts at home or whatever, but I have for some years been willing to loan out lenses to local colleagues to try and so forth. I think that is the best way to put one's money where one's mouth is. Anybody within driving distance of me should know that they can come over and see for themselves. I did not keep the rb 50 though, so you'll have to try that somewhere else!
I would not dispute that different people will pick different lenses. As I say, the only lens I ever had issues with was the 50; I researched it and discovered that there is a broad consensus that the rz 50 uld is better, so I don't think my findings were unusual.